This invention relates to a hydrophobe-containing alkali soluble or swellable copolymer thickener prepared from an ethylenically unsaturated copolymerizable surfactant monomer having a cloud point of 65xc2x0 C. to 95xc2x0 C. Aqueous compositions utilizing the copolymer exhibit constant or increased viscosity at temperatures approaching 120xc2x0 C.
Alkali soluble polymeric thickeners are described in U.S. Pat. No. 4,384,096, U.S. Re. Pat. No. 33,156, and U.S. Pat. Nos. 4,616,074, 4,384,096 describes alkali soluble polymeric thickeners which are aqueous emulsion copolymers of a xcex1,xcex2-ethylenically unsaturated carboxylic acid monomer, a nonionic xcex1,xcex2-ethylenically unsaturated comonomer, and a copolymerizable nonionic vinyl surfactant esters. U.S. Re. Pat. No. 33,156 describes alkali soluble polymeric thickeners which are aqueous emulsion copolymers of a xcex1,xcex2-ethylenically unsaturated carboxylic acid monomer, a nonionic xcex1,xcex2-ethylenically unsaturated monomer, and a nonionic urethane monomer. U.S. Pat. No. 4,616,074 describes alkali soluble polymeric thickeners which are aqueous emulsion copolymers of an addition copolymerizable substituted methylene succinic acid ester surfactant monomer, an xcex1,xcex2-ethylenically unsaturated carboxylic acid monomer, and a nonionic xcex1,xcex2-ethylenically unsaturated monomer.
The disadvantage of the above described alkali soluble polymeric thickeners is that at temperatures as low as 25xc2x0 C., the viscosity of the thickeners begins to decrease and continues to decrease at an increasing rate as the temperature is further increased. Such decreasing viscosity properties exhibited by the thickeners at elevated temperatures severely limits the choice of applications for the alkali soluble thickeners. Therefore, it would be advantageous to develop a thickener wherein the viscosity of the thickener does not decrease at elevated temperatures.
Accordingly, it is an object of the invention to provide an alkali soluble or swellable thickened aqueous composition.
It is another object of the invention to provide a thickened aqueous composition in which the viscosity of the composition does not decrease at elevated temperatures.
It is also an object of the invention to provide a thickened aqueous composition in which the viscosity of the composition is constant or increases while being exposed to elevated temperatures.
With regard to the foregoing and other objects, the present invention provides a hydrophobe-containing alkali soluble or swellable copolymer thickener which provides aqueous compositions with constant or increased viscosity at temperatures approaching 120xc2x0 C., wherein said copolymer comprises an emulsion polymerization product of
(A) from about 0.1 to about 25 weight percent, based on the total weight of the copolymer, of an ethylenically unsaturated copolymerizable surfactant monomer having a cloud point of from about 65xc2x0 C. to about 95xc2x0 C., wherein the surfactant monomer has the formula
M(EO)x(PO)y(BO)zOR1
wherein M is a residue selected from the group consisting of an ethylenically unsaturated carboxylic acid, ethylenically unsaturated dicarboxylic acid, and a copolymerizable isocyanate; EO is an ethylene oxide unit; PO is a propylene oxide unit; BO is a butylene oxide unit; x is from 10 to 45; y is from 0 to 35; z is from 0 to 35; provided that x+y+z is from 20 to 45; and R1 is selected from the group consisting of alkyl, alkylene, cycloalkyl, cycloalkylene, and arylalkyl group wherein the alkyl group has 1 to 30 carbon atoms;
(B) from about 20 to about 70 weight percent, based on the total weight of the copolymer, of an xcex1,xcex2-ethylenically unsaturated monocarboxylic acid monomer having the formula 
wherein R2 is selected from the group consisting of hydrogen, an alkyl group having 1 to 4 carbon atoms, and xe2x80x94CH2COOR3; and R3 is hydrogen or an alkyl group having 1 to 4 carbon atoms; and
(C) from about 10 to about 70 weight percent, based on the total weight of the copolymer, of a nonionic xcex1,xcex2-ethylenically unsaturated monomer having the formula
CH2xe2x95x90CR4R5
wherein R4 is selected from the group consisting of hydrogen, methyl and Cl; and R5 is selected from the group consisting of CN, Cl, xe2x80x94COOR6, xe2x80x94C6H4R7, xe2x80x94CHxe2x95x90CH2, 
wherein R6 is selected from the group consisting of hydrogen, Cl, Br, and an alkyl group having 1 to 4 carbon atoms; R7 is an alkyl group having 1 to 12 carbon atoms or a hydroxyalkyl group having 2 to 8 carbon atoms; and R8 is an alkyl group having 1 to 8 carbon atoms.
According to another aspect the invention provides a method for making a thickened aqueous composition wherein said method comprises: (I) preparing a copolymer as described above; (II) combining the copolymer prepared in Step (I) with a composition comprising water at a pH of from about 2 to about 5 to form an aqueous copolymer dispersion; and (III) at least partially neutralizing said aqueous copolymer dispersion prepared in Step (II) to a pH of at least about 5.5 to form a hydrophobe-containing alkali soluble or swellable thickened aqueous composition which exhibits constant or increased viscosity at temperatures approaching 120xc2x0 C.
The hydrophobe-containing alkali soluble or swellable copolymer thickeners of the invention thicken aqueous compositions and maintain or increase the viscosity of the thickened aqueous composition at temperatures approaching 120xc2x0 C. Thus, the copolymer thickeners of the invention exhibit enhanced thickening efficiency in comparison with prior art copolymers. In addition, a reduced quantity of copolymer thickener is required to achieve a fixed level of thickening in comparison with the amount of prior art thickeners.